iommu/arm-smmu: Tear down domain context if attach fails

Currently we're leaving domains half-initialized after a
partially-successful attach.  Fix this by destroying the
domain in the error path.

Change-Id: I36c529ed4974c01fba96088b6f57a8e82b350252
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>